Bushing assembly for electrical apparatus



Oct. 13, 1964 A. s. LINDwAY ETAL 3,l53,114

BusHING AssEMBLY FOR ELEc'rRIcAL APPARATUS Filed Jan. 24. 1962 UnitedStates Patent O 3,153,1M BUSHNG ASSEMELY FR ELECTRCL AiblAff/TUS AndrewS. lLindway .and .Iohn MI. Anderson, Pittshurgh,

Pa., assignors to Aiiis-Chainiers Manufacturing Cornpanfl, Milwaukee,Wis.

Filed Ian. 24, 13%2, Ser. No. 169,706 Ki Ciarns. (Cl. 1714-43) Thisinvention relates to electrical insulating bushings and in particular toinsulating bushings rnounted in a tank containing an electricalapparatus innnersed in a dielectric liquid.

In a number of instances it is standard practice to house an electricalapparatus in a tank substantially filled with a dielectric liquid. Thecommon example is a distribution transforrner contained in an oil filledtank. The electrical leads to the transforrner are brought through thetank walls and require insulating bushings at their points of entry.These bushings may be made of a ceramic material such as porcelain andconsequently, are subject to damage in the field. In structures of theprior art, replacement of a damaged bushing has not been a simple task.Freqnently, it is necessary to locate the insulating bushings below thelevel of the dielectric liquid in the tank containing the apparatus.Consequently, replacement of the damaged bushing first calls forrenioving the dielectric liquid from the tank to a level below theinsulating bushing. If the liquid is not partially removed from the tankit is apparent that it would leak through the opening in the tank wallafter the bushing has been removed.

The above type of transforrner also normally uses protective fuses.These fuses may comprise a part of the electrical leads attached to thewindings of the transformer. In order that the fuses are partiallyresponsive to the temperatures of the dielectric liquid, they are placedwithin the transformer tank and subrnerged in the dielectric liquid. Itis, of course, to be expected that these fuses will have to be replacedoccasionally while the transformer is in the field. The manner in whichthese fuses can be replaced is somewhat related to the above describedproblem of replacing damaged insulating bushings. A conventional meansfor gaining access to the protective fuse is the provision of a handholein the cover of the transformer tank. The handhole has a removable coverand the maintenance man may remove this cover and then fish for thedamaged fuse which is positioned below the level of the oil. An atternptto gain access to the fuse through the side of the tank would meanpartial draining of the oil.

Our invention comprises a novel bushing arrangement which simplifiesboth of the above described problems of replacing damaged bushings andprotective fuses. Briefly described, our bushing comprises two Sectionsthrough which an electrical lead extends. When the external section ofthe bushing requires replacement, its removal causes a biased meanscoupled to theelectrical lead to be released. The released biasing meansforces a sealing device which is also mounted on the electrical lead toseal off all openings in the interior bushing section through which thedielectric liquid would otherwise escape. The protective fuse may form aremovable section of the electrical lead and thereby easily be replacedwhile the sealing means prevents leakage of the dielectric liquid.

lt is, therefore,,one object of this invention to provide a new andimproved insulating bushing.

Another object of this invention is to provide a new and improved meansfor readily replacing the exterior portion of the damaged insulatingbushing.

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Another object of this invention is to provide a new and improved meansfor readily replacing the protective fuse contained within an electricalapparatus.

Objects and advantages other than those mentioned above will becomeapparent upon readint7 the description in connection with the drawing inwhich:

FIG. 1 illustrates an electrical apparatus containing a bushing of thisinvention;

FIG. 2 is a view of the bushing and fuse arrangement of this inventiontaken in section along its axis;

PIG. 3 is a sectional view taken along' line iii-Hi of PIG. 1; and

' FIG. 4 is a sectional view of the bushing and fuse arrangement of thisinvention in a modified form.

Referring to FIG. l, a distribution transformer lit is illustratedcontaining an insnlating bushing 12 which is horizontally mounted belowthe level of `a dielectric liquid 14 in a tank 16. As can be seen fromthe detailed illustration of PIG. 2, the bushing 12 comprises anexterior section 18 and an interior section 19. The eX- terior sectionmay be mounted to a wall 21 of the tank through a conventional clamp 23and bolts 24 (see FIG. 3) and sealcd about an opening 26 of the wall bya gasket 27 which is compressed when the bolts and clamp are securedtightly. The interior section 19 may have fianges 29through which bolts30 extend for engaging threaded lugs 31 on the interior side of the tankwall 21. The interior bushing section 19 is forced against a gasket 32for preventing oil leakage at its junction with the tank wall. Bothbushing Sections are hollow in order to receive an electrical conductor34 which partially comprises a rigid rod 36 with a threaded end 37. Therod 36 is maintained in its relative position with the exterior bushingsection 18 by means of an annular cap 39 whichis in sealing engagernentwith the bu'shing and a nut dt) which is threaded on the rod 315 againstthe cap. `Also threaded on the rod is a connector 42 to which a flexiblelead 44 is connected. A gasket 45 is seated between cap 39 and bushingsection 18.

The electrical conductor 34 within the two bushing Sections furthercomprises a removable protective fuse 4G with one end secured to the rod35 by a removable roll pin 47. The other end of the fuse has aconventional right angle slotted groove or track 50 for engaging a lug51 in anelectrically conductive fuse holder 53. Connected to theopposite end of the fuse holder is a transforrner winding lead 54.

At an intermediate point in the fuse holder 53 a means 55 has beenprovided for securing it to a truncated, conical or tapered insulatingsleeve 57. The end 59 of the fnse holder is slidably mounted in the end6% of the interior section through an opening 61. Fuse holder end 51?may be hexagonally shaped to prevent any relative rotation with end'titi and its opening ef which is also hexagonal. A biased spring ispositioned between an extension od of the inner bushing section 19 andthe broad end 65 of the sleeve 57. This spring is inaintained in itsbiased condition by the action of the nut 4d on the condnctor rod 36.Holes 66 displaced along the longitndinal, surfaces of the bushinginterior section w and the sleeve 57 perrnit the passage of oil.Consequently, fuse is surrounded by the oil and is subject to thetemperature of the oil, a desirable feature. It is apparent that if theouter bushing section is removed and the sleeve and inner bushingsection reman inptheir illustrated positions, oil will pass through theholes 65 in these two members and leak through the opening 26 in thetank wall. .Thus, it becomes necessary to seal off all entry spaces inthe interior bushing section 19.

Assuming that the exterior bushing section lt; needs Co be replaced, theabove sealing requirements can be awaria accomplished in the followingmanner. The threaded connector 42. is first removed from the conductorrod 36 and then the nut 40 is backed off and removed. Recalling that theSpring 63 is in a biased condition it can be Seen that a force isexerted to the right or inwardly on the electrical conductor through thehollow sleeve 57 and fuse holder 522. Thus, as nut :to is baclted offspring 63 expands and, since it is coupled to the conductor throughslceve 57, the conductor is moved inwardly until the sleeves outersurface makes contact with the inner surface 69 of the interior bushingsection. The dimensions of the sleeve and interior 'eushing section areSo designed as to pcrmit physical contact with each other only aftereach covers the holes od in the other. T hus, entrance of the oilthrough the holes in the interior section and sleeve is blocked. Whileoil may enter through the interior bushing section end od, furthertransmittal of this is blocked by the abutment of the Sleeve against endoil.

After nut 4% has been removed from conductor rod TK and a sealing actionhas been achieved, disassembly of the extcrior bushing section ll andits Cap may commence. Upon removal of the clamp bolts, a new bushingsection may then be installed. Retightening the nut 40 causes theconductor 34 and its fuse 46, along With the hollow sleeve 57, to bemoved outwardly against the spring 63 to bias it and permit entry of oilthrough the holes If it is only necessary to replace the protective fuse46 and not the bushingls exterior section the above Steps for obtaininga Sealing action are repeated while the exterior section iS stillclamped to the tani: wall The conductor rod So is then rotatcd a quarterof a turn through the provision of a slot '71 at its end. This rotationdisengages the fuse from its fuse holder S3 and the rod and itsconnected fuse may then be removed from the bushing. The roll pin 47 isrelnoved and a new fuse connected to the rod. The rod and its connectedfuse are then ready for reassembly in the bushing.

The modified bushing arrangement shown in FlG. 4 has, as one significantdifference, the fact that it is designed only for externally replacingthe protective fuse 46 and is not designed for replacement of theexterior bushing section 18 in a manner similar to the abovearrangement.

Another difference is that the interior Section 19 does not have anycirculating holes do and the oil which comes in contact With theprotective fuse enters only through end oil of the section 19.Consequently, there is no need for the hollow Sleeve 57 of the bushingshown in PIG. 2. Since the exterior bushing section 18 is not intendedto be replaced without lowering the level of the dielectric liquid,there is no need for the interior section 19 to abut in a sealingarrangement with the tanlr wall In fact, it is conceivable that onecould combine the two Sections into an integral unit without departingfrom the spirit of this invention.

At the end 6d of the interior section 19 a recessed Shoulder '73 isprovided. Positioned on this Shoulder is a biased spiral compressionspring 63' which is coupled to the conductor 34 by a washer 'F5 andseveral nuts 76 threaded on a conductor stud *29. The conductor stud isof a size to freely move in an axial direction through end 6d of theinterior section and the washer 75. The conductor Stud '79 has aShoulder Et) for bearing against a gasket S2 which is mounted about theStud end The fuse holder 53 is threaded on end i of the Stud. lt is tobe noted that a pair of projections 85 extend from opposite sides of thefuse holder. These projections engage with longitudinal grooves in theinterior busning section 19. The combination of the projections 85 ingrooves S6 prevents rotation of the fuse holder when the conductor rod36 is being rotated to disengage the fuse 46 from its holder 53.

Replacement of a blown fuse is substantially the same as in the firstdescribed bushing structure. Upon removal of the nut 4d the spring 63exnands and causcs its adjacent washer and the conductor to moveinwardly to the right. This movement is stop-ped when the gasliet S2 isin contact with end of) of the inner section This prevents all passageof oil through oeening 26 in the tank wall and permits one to replacethe protective fuse with relative ease.

While only two embodiments of this invention have been illustrated anddescribed, it will be apparent to those skilled in the art thatadditional modifications may be made without departing from the Spiritof this invention and the scope of the appended claims.

l-laving now particularly described and ascertained the nature of oursaid invcntion and the manner in which it is to be performcd, we declarethat what we claim is:

1. A bushing of the type that cxtends in Sealing relationship throughthe wall of a tank containing electrical apparatus immersed in adielectric liquid, comprising,

a hollow exterior extension mountable outside the tank,

a hollow interior extension mountable inside the tank, said interiorextension having an inwardly tapering surface, said surface having ahole connecting the interior of the bushing to receive dielectric liquidfrom the tank,

a conductor cxtending through said bushing cxtensions in an axiallyslidable relationship,

sealing means axially movable within said interior extension betweeninward position and an outward position, said sealing means comprising ahollow sleeve having an outer Surface and a hole on said surface foradmitting the liquid; said outer surface being Shaped to be parallel tsaid inner surface and to be spaced from said inner surface When saidsleeve is in said outward position and to abut said inner surface toclose the interior of said bushing from said tank when said sleeve is inits relatively inward position,

means on said conductor for engaging said sealing means whereby saidsealing means is positionable according to the axial position of saidconductor,

ias means mounted between said interior extension and said sealing meansto urge said sealing means inwardly, and

exteriorly accessible means for fastening the outer end of Saidconductor to said exterior extension, said means being opera'ole duringunfastening to release said conduetor to move inwardly whereby said biasmeans positions said sealing means to Seal the interior of said bushingfrom said tank, Said means being operable during fastening to move saidconductor outwardly whereby Said sealing means is positione to admitliquid from Said tank to Said bushlng interior.

2. A bushing according to claim 1 in which said bias means comprises aspiral spring encircling said conductor and positioned between a fiangeof Said interior extension and an end of Said slceve.

3. A bushing according to claim 1 in which said conductor includes aremovable fuse.

4. A bushing according to claim 1 in which said exteriorly accessiblefastening means maintains said bushing substantially sealed until Saidconductor has been released sufiiciently to cause said sealing means tocover said hole.

References Cited in the file of this patent UNITED STATES PATENTS2,026,196 Stephens Dec. 31, 1935 2,647,939 Palucv Aug. 4J 1953 FOREIGNPATENTS 575,058 Great Britain Feb. 1, 1946 565,677 Canada Nov. 4, 1958

1. A BUSHING OF THE TYPE THAT EXTENDS IN SEALING RELATIONSHIP THROUGHTHE WALL OF A TANK CONTAINING ELECTRICAL APPARATUS IMMERSED IN ADIELECTRIC LIQUID, COMPRISING, A HOLLOW EXTERIOR EXTENSION MOUNTABLEOUTSIDE THE TANK, A HOLLOW INTERIOR EXTENSION MOUNTABLE INSIDE THE TANK,SAID INTERIOR EXTENSION HAVING AN INWARDLY TAPERING SURFACE, SAIDSURFACE HAVING A HOLE CONNECTING THE INTERIOR OF THE BUSHING TO RECEIVEDIELECTRIC LIQUID FROM THE TANK, A CONDUCTOR EXTENDING THROUGH SAIDBUSHING EXTENSIONS IN AN AXIALLY SLIDABLE RELATIONSHIP, SEALING MEANSAXIALLY MOVABLE WITHIN SAID INTERIOR EXTENSION BETWEEN AN INWARDPOSITION AND AN OUTWARD POSITION, SAID SEALING MEANS COMPRISING A HOLLOWSLEEVE HAVING AN OUTER SURFACE AND A HOLE ON SAID SURFACE FOR ADMITTINGTHE LIQUID; SAID OUTER SURFACE BEING SHAPED TO BE PARALLEL TO SAID INNERSURFACE AND TO BE SPACED FROM SAID INNER SURFACE WHEN SAID SLEEVE IS INSAID OUTWARD POSITION AND TO ABUT SAID INNER SURFACE TO CLOSE THEINTERIOR OF SAID BUSHING FROM SAID TANK WHEN SAID SLEEVE IS IN ITSRELATIVELY INWARD POSITION, MEANS ON SAID CONDUCTOR FOR ENGAGING SAIDSEALING MEANS WHEREBY SAID SEALING MEANS IS POSITIONABLE ACCORDING TOTHE AXIAL POSITION OF SAID CONDUCTOR, BIAS MEANS MOUNTED BETWEEN SAIDINTERIOR EXTENSION AND SAID SEALING MEANS TO URGE SAID SEALING MEANSINWARDLY, AND EXTERIORLY ACCESSIBLE MEANS FOR FASTENING THE OUTER END OFSAID CONDUCTOR TO SAID EXTERIOR EXTENSION, SAID MEANS BEING OPERABLEDURING UNFASTENING TO RELEASE SAID CONDUCTOR TO MOVE INWARDLY WHEREBYSAID BIAS MEANS POSITIONS SAID SEALING MEANS TO SEAL THE INTERIOR OFSAID BUSHING FROM SAID TANK, SAID MEANS BEING OPERABLE DURING FASTENINGTO MOVE SAID CONDUCTOR OUTWARDLY WHEREBY SAID SEALING MEANS ISPOSITIONED TO ADMIT LIQUID FROM SAID TANK TO SAID BUSHING INTERIOR.